The present invention relates to magnetic tape recording. More particularly, the present invention relates to a multi-channel magnetic tape recording system employing an optical tracking servo to sense and correct for lateral tape motion, and lateral track motion, as the tape is drawn longitudinally across a head transducer assembly.
Digital tape recording remains a viable solution for storage of massive amounts of data. Conventionally, at least two approaches are employed for recording of digital information onto magnetic recording tape. One approach calls for moving the tape past a rotating head structure which records and plays back user information from discontinuous transverse tracks. Interactive servo systems are employed to synchronize rotation of the head structure with travel of the tape. Another approach is to draw the tape across a non-rotating head at a considerable linear velocity. This approach is sometimes referred to as linear xe2x80x9cstreamingxe2x80x9d tape recording and playback.
Increased data storage capacity, and retrieval performance, is being required of all commercially viable mass storage devices and media. In the case of linear tape recording a popular trend is toward multi-head, multi-channel fixed head structures with narrowed recording gaps and track widths so that many linear tracks may be achieved on a tape medium of predetermined width, such as one-half inch width tape. Tape substrates are also being made thinner, with increased tape lengths being made possible in small diameter reel packages.
Because of a relatively high linear tape velocity, and because tape substrates continue to be made thinner and thinner, guiding tape past a tape head structure along an accurate invariant linear path has proven to be highly problematical. One error phenomena is known as xe2x80x9clateral tape motionxe2x80x9d or xe2x80x9cLTMxe2x80x9d. LTM is a major source of tracking errors in linear tape recording. One approach to minimizing LTM tracking errors is to provide a multi-roller tape guide structure, such as the type described in commonly assigned U.S. Pat. No. 5,414,585 entitled: xe2x80x9cRotating Tape Edge Guidexe2x80x9d, the disclosure thereof being incorporated herein by reference. While this approach has provided a viable xe2x80x9copen loopxe2x80x9d solution to LTM, with the advent of new head technologies, such as magneto-resistive read heads, and new higher coercivity recording media, track widths may be very small, and many additional tracks may be defined on the tape. Unfortunately, a limiting factor is LTM, and at some track width dimension and track density, it is not possible to follow the tape accurately enough to provide reliable performance.
One solution to correction for LTM has been to record or pre-record magnetic servo tracks (i.e. xe2x80x9cservowritexe2x80x9d) onto the tape before it reaches the user. These tapes are known in the art as xe2x80x9cpreformattedxe2x80x9d tapes, and the step of recording accurate servo tracks onto the tape is both time consuming and expensive. Examples of tape systems employing preformatted tapes are given by U.S. Pat. No. 5,432,652 entitled: xe2x80x9cServo and Data Format for Magnetic Tape Having Plural Spaced-Apart Servo Areas Interleaved with Data Track Areas Having Serpentine Track Scanning Using Any One of a Plurality of Number of Concurrently Accessed Tracks.xe2x80x9d Another example is provided by U.S. Pat. No. 5,675,448 entitled: xe2x80x9cTrack Pitch Error Compensation System for Data Cartridge Tape Drivesxe2x80x9d.
Once the decision has been made to provide separate magnetic servo tracks or to embed servo information within the magnetic user data tracks recorded onto the tape, a suitable coarse position/fine position actuator mechanism must be added to the tape drive. One example of a stepper motor/voice coil actuator is provided by U.S. Pat. No. 5,280,402 entitled: xe2x80x9cCombined Stepper Motor and Voice Coil Head Positioning Apparatusxe2x80x9d.
Optical servo tracks have been provided within floppy disks. One example of a floppy disk and compatible drive is given in U.S. Pat. No. 5,065,387 entitled: xe2x80x9cMethod and Apparatus for Generating Tracking Error Signals by Means of an Optical Servo Systemxe2x80x9d, the disclosure thereof being incorporated herein by reference.
While these prior methods and approaches have worked within their intended applications and uses, improvements and simplifications in the medium and drive apparatus have been lacking. Accordingly, a hitherto unsolved need has remained for a multi-track, multi-channel digital streaming tape system which overcomes limitations and drawbacks of the known prior approaches.
A general object of the present invention is to provide a tape recording system and recording tape with an optical servo pattern to enable correction of LTM in a manner overcoming limitations and drawbacks of the prior art.
In accordance with one aspect of the present invention a linear magnetic tape medium has a first surface accessible by a laterally positionable, multi-head magnetic read/write transducer assembly, and a second surface accessible by an optical servo transducer assembly physically coupled to the magnetic read/write transducer assembly. A multiplicity of linear data tracks are defined on the first surface. Each linear track provides storage of magnetic data patterns written by a head of said magnetic read/write transducer positioned and maintained thereat by a lateral head positioner. A multiplicity of linearly extending servo features are formed on the second surface and are read by the optical servo transducer which generates a servo feedback signal to aid track following in the presence of lateral tape motion by the magnetic read/write transducer as the tape medium is drawn linearly there across.
These and other objects, aspects, advantages and features of the invention will be more fully understood and appreciated upon considering the following detailed description of a preferred embodiment presented in conjunction with the accompanying drawings.